Dissertations and Theses

Date of Award


Document Type



Biomedical Engineering

First Advisor

Susannah P. Fritton

Second Advisor

Mitchell B. Schaffler

Third Advisor

Luis Cardoso


Muscle, Botox, Disuse, Osteocyte, Bone


Mechanical loading is essential for maintaining bone tissue. Reduced mechanical loading has been shown to have a negative effect on bone, and can result in the development of disuse osteoporosis. Disuse models of muscle inactivity and immobilization, like the Botox model used in this study, result in changes in the bone microarchitecture, the mechanisms behind which are not fully understood. In a previous four-week Botox disuse study, skeletally mature 20- week-old rats experienced degradation of intracortical bone, increased vascular porosity, and decreased osteocyte lacunar density in the tibiae. The focus of this study was to explicate a potential source of these differences and determine if changes in gait, muscle gene expression, and markers of osteocyte activity could be detected as early as one week after Botox-induced muscle paralysis. In the present study, 20-week-old female rats were injected with botulinum toxin A (BTX, n=12) in the right hindlimb muscles, while external control rats (CTRL, n=12) were similarly injected using a saline solution. Animals then underwent gait and digit analyses to quantify the degree of paralysis. One-week post-injection, osteocyte expression of sclerostin (Scl), osteocyte apoptosis (caspase-3), perilacunar remodelling (cathepsin K), and staining of vascular pores and mast cells were assessed using immunohistochemistry. Real-time polymerase chain reaction (qPCR) was performed on the quadriceps muscles to assess relative expression differences for several musculoskeletal-related genes (Tgf-β1, Mstn/Gdf-8, Fgf-2, and Igf-1). After one week of disuse, Botox-injected rats had a decrease in gait ability of ~75% and decreased digit abduction. Quadriceps and calf muscles showed a significant reduction in muscle mass (>20%) in the BTX group compared to CTRL. While there were only a few localized iv changes in osteocyte activity, the muscle relative genetic expression analysis showed increased relative gene expression of myostatin in BTX left versus BTX right (injected) and both CTRL limbs, indicating a potential systemic effect of Botox and/or disuse.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.